The driving wheel is the wheel on a vehicle or machine which is tasked with propelling the machine. In vehicles with positive traction drive axles, the driving wheel is both wheels on the drive axle. In most vehicles manufactured prior to 1986 worldwide, the driving wheel is on the front of the vehicle. In rear-wheel drive vehicles, the driving wheel is on the right side of the rear axle. On most heavy trucks, the driving wheel is located on the first axle on the rear of the truck. In trucks with a single axle on the rear, the right side wheel is the one that receives the power in normal driving conditions.
In most high-performance and racing applications, the vehicle will utilize a locked rear differential or a spool. The locked differential and spool are devices which lock both sides of the drive axle. This makes it possible for both drive wheels to have traction under abrupt acceleration. This is done in an attempt to gain the most speed by eliminating the tire slip found in an open or stock production differential.
In most four-wheel drive vehicles, the driving wheel is on the rear axle unless the vehicle has its transfer case locked into four-wheel drive mode. In most cases, four-wheel drive is actually two-wheel drive with one front and one rear wheel receiving power to propel the vehicle. In extreme off-road vehicles, both the front and rear axles are locked, sending power to all four tires. This is a true four-wheel drive vehicle.
In locomotive use, the first locomotive in a chain of locomotives typically controls the driving wheel. Power is supplied to the electric traction motor by the generator mounted behind the diesel power plant in the locomotive. The electric driving wheel is controlled by the engineer who controls the amount of power directed to the traction motor. In modern locomotives, the train can be powered by a diesel at both the front and rear of the train. The pusher locomotive is a diesel locomotive positioned at the rear of the train. The engineer in the front diesel controls the pusher diesel by remote control. The purpose is to eliminate the slack typical in a train. By controlling the slack or the amount of stretch from the car's hitching knuckles, the train can operate with better fuel economy. By placing the driving wheel at both ends of the train, it is being both pulled and pushed.